Preparation Preheat broiler. Line baking sheet with aluminum foil. Arrange tomatillos and jalapeño chile on prepared baking sheet. Broil until tomatillos and jalapeño chile are soft and blackened in spots, about 5 minutes per side. Cool; transfer tomatillos, jalapeño chile, and any juices on baking sheet to blender. Add fresh mint and lime juice; blend to coarse puree. Transfer mixture to bowl; mix in chopped onion. Season salsa with salt.